The invention relates to control of a throttle plate in a throttle body for an internal combustion engine in which an electric motor actuates the throttle plate.
In an internal combustion engine, it is known design practice to use a throttle body that controls distribution of air from an engine air intake to an intake manifold for the engine cylinders. The throttle body contains an adjustable throttle plate carried by a throttle shaft. The position of the throttle plate is controlled by a driver-controlled linkage mechanism connected to the vehicle accelerator pedal. It also is known design practice to use an electronic throttle body wherein the angularity of the throttle plate is activated by an electric motor under the control of a microprocessor.
A throttle return spring is used to bias normally the throttle plate toward a closed position. The electric motor, as it adjusts the angularity of the throttle plate, thus must overcome the force of the spring that tends to close the throttle plate.
Even if a return spring were not present in the throttle body, a motor controlled throttle plate would be close to a closed position when the engine is shut down with the accelerator pedal relaxed. This creates a condition that is conducive to the development of icing at the periphery of the throttle plate. In order to break the throttle plate loose from its frozen position when the engine is restarted, the motor must be capable of developing a high initial torque. The torque capacity of the motor thus must be designed to accommodate this maximum torque condition. Further, the motor would be larger and its cost greater because of this requirement to protect the system against freezing conditions.
A freezing condition of the throttle plate can occur during operation of the engine at minimal throttle setting as air flow across the margin of the throttle plate experiences a venturi effect, which reduces the air pressure at the margin and induces condensation of water vapor present in the air. Under certain operating conditions, the condensation can freeze, thereby locking the throttle plate to the surrounding wall of the throttle body. Further, throttle plate sticking at closed throttle may occur if the throttle plate or the wall surrounding the throttle plate is coated with environmental debris or hydrocarbon deposits.
An example of a controller for a throttle valve for adjusting the throttle plate position to a partly open position is disclosed in U.S. Pat. No. 5,735,243. The throttle body disclosed in the ""243 patent has a redundant throttle plate control involving the use of an electric motor that is geared to a throttle shaft as well as a mechanical actuator under the control of a vehicle operator. As the operator adjusts the accelerator pedal, a return spring is used to oppose the torque of the electric motor. A relief spring, which opposes the force of the return spring, adjusts the throttle plate to a slightly open position when the engine is shut down or when the motor has been deactivated. The biasing force of the release spring is greater than the biasing force of the return spring so that the throttle blade will remain slightly open.
A similar spring system for adjusting the throttle plate to a so-called xe2x80x9crestxe2x80x9d position is disclosed in U.S. Pat. No. 4,947,815. As in the case of the system of the ""243 patent, the system of the ""815 patent has a return spring and a counteracting spring acting on the throttle shaft. Counteracting spring forces developed by the springs complement the torque developed by an electric motor. Thus, when the electric motor fails due to a loss of voltage, for example, the throttle may be set to a partially open position so that the driver of the vehicle can drive the vehicle to an emergency repair location.
U.S. Pat. No. 5,078,110 discloses a throttle valve arrangement wherein provision is made for detecting a jammed or frozen actuator. A desired throttle position signal is distributed to a microprocessor, which has control logic that compares the desired position signal to an actual position signal. If there is a difference between the two signals, jamming is detected. Provision is made for releasing the jamming by adjusting the pulse duty factor of the electric motor that activates the throttle plate. Torque is increased and decreased within a defined time interval to release the jammed actuator.
The improved throttle body assembly of the invention includes a small electric motor for driving the throttle plate throughout its range of angular positions. The motor is under the control of a microprocessor. Unlike most prior art constructions, a return spring is not used for normally biasing the throttle plate to its closed position. The elimination of a return spring protects the throttle plate against freezing and makes it possible to design the motor with a significantly lower torque rating. This reduces the overall cost and makes it more feasible to design the throttle body into a smaller assembly, which makes it easier to package the throttle body in an engine compartment of a passenger vehicle.
A microprocessor responds to the position of the vehicle accelerator pedal under the control of the vehicle operator to control the motor. It responds further to a signal from the engine ignition that indicates when the engine has been turned off.
The microprocessor activates the motor when the engine is shut down by issuing a command to the electronic throttle body to activate the throttle plate to an open setting, such as about a one-quarter throttle setting or greater. By positioning the throttle plate in this fashion during engine-off soak, the throttle plate freezing condition is avoided.
In practicing the invention, a throttle position sensor is used to develop an actual throttle position. An ignition switch for the engine develops an engine shutdown signal.
An accelerator pedal position sensor develops an actual accelerator position signal. The microprocessor develops a throttle motor control signal responsive to the presence of an engine shutdown signal to partly open the throttle plate when the engine is shut down.
An additional advantage of the invention is the ability of the reduced capacity throttle motor to actuate the throttle plate even if the wall of the throttle body surrounding the throttle plate is coated with environmental debris or hydrocarbon deposits.